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Applied and Environmental Microbiology, March 2005, p. 1169-1177, Vol. 71, No. 3
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.3.1169-1177.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Biosynthesis of Auxin by the Gram-Positive Phytopathogen Rhodococcus fascians Is Controlled by Compounds Specific to Infected Plant Tissues

Olivier Vandeputte,¹ Sevgi Öden,² Adeline Mol,¹ Danny Vereecke,³ Koen Goethals,³ Mondher El Jaziri,^1* and Els Prinsen²

Laboratory of Plant Biotechnology, Université Libre de Bruxelles, Brussels,¹ Department of Biology, University of Antwerp, Antwerp,² Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, Ghent, Belgium³

Received 5 July 2004/ Accepted 11 October 2004

The role and metabolism of indole-3-acetic acid in gram-negative bacteria is well documented, but little is known about indole-3-acetic acid biosynthesis and regulation in gram-positive bacteria. The phytopathogen Rhodococcus fascians, a gram-positive organism, incites diverse developmental alterations, such as leafy galls, on a wide range of plants. Phenotypic analysis of a leafy gall suggests that auxin may play an important role in the development of the symptoms. We show here for the first time that R. fascians produces and secretes the auxin indole-3-acetic acid. Interestingly, whereas noninfected-tobacco extracts have no effect, indole-3-acetic acid synthesis is highly induced in the presence of infected-tobacco extracts when tryptophan is not limiting. Indole-3-acetic acid production by a plasmid-free strain shows that the biosynthetic genes are located on the bacterial chromosome, although plasmid-encoded genes contribute to the kinetics and regulation of indole-3-acetic acid biosynthesis. The indole-3-acetic acid intermediates present in bacterial cells and secreted into the growth media show that the main biosynthetic route used by R. fascians is the indole-3-pyruvic acid pathway with a possible rate-limiting role for indole-3-ethanol. The relationship between indole-3-acetic acid production and the symptoms induced by R. fascians is discussed.

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* Corresponding author. Mailing address: Laboratory of Plant Biotechnology, Université Libre de Bruxelles, 1850 Chaussée de Wavre, B-1160 Brussels, Belgium. Phone: 32(0)2-650-9181. Fax: 32(0)2-650-9175. E-mail: jaziri{at}ulb.ac.be.

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Applied and Environmental Microbiology, March 2005, p. 1169-1177, Vol. 71, No. 3
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.3.1169-1177.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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